A first principle study of SO3 decomposition on silver nano-clusters: Implications toward hydrogen production

In this work, based on first principles density functional theory, we have investigated the interaction of SO3 molecule on three different substrates; (i) clean Al2O3 surface (0001) (ii) an isolated Ag6 cluster and (iii) Ag6 clusters deposited on the Al2O3 surface. All calculations were carried out using the plane wave based pseudopotential method under the framework of density functional theory. For the clean Al2O3 surface, the SO3 molecule was adsorbed in parallel orientation on the surface resulting in an elongation of the S–O bond from 1.44 to 1.52 Å with interaction energy of 1.67 eV. In contrast, the interaction of SO3 with Ag6 was found to be weak with 0.4 eV interaction energy and 1.47 Å as the largest S–O bond length. Remarkably, when SO3 molecule interacted with Ag6 cluster deposited on the Al2O3 support, the binding was found to be higher than both Al2O3 and Ag6 clusters in their isolated state. In particular, upon adsorption of SO3 on Ag6/@Al2O3, the S–O bond length was found to increases from 1.44 to 1.64 Å and the interaction energy was estimated to be 2.00 eV. As the bond elongation bears the signature of bond weakening, a comparison of the above three results clearly suggests that the dissociation barrier of S–O bond on the Ag6@Al2O3 support will be significantly lower than that on the isolated Ag6 or Al2O3 surface. The nature of chemical interaction of SO3 on these three systems has been discussed based on the electronic density of states analysis.